House Democrats this year matched Republican fund-raising in key contests, helping to hold down losses in a year when President Reagan won reelection by an overwhelming margin.

In an election where Senate candidates broke records spending money -- including more than $25 for every vote won by Sen.-elect John D. (Jay) Rockefeller IV (D-W.Va.) -- the most significant political development may be the success of House Democrats in raising money and distributing it properly.

In contrast to the 1980 and 1982 elections, an analysis of the cash flow in close House contests shows that most Democratic candidates, including those running for open seats and as challengers to GOP incumbents, had adquate financing.

Some of the Democratic fund-raising success apparently can be attributed to Rep. Tony Coelho (D-Calif.), chairman of the Democratic Congressional Campaign Committee. Coelho mounted a campaign to increase the cash raised by his committee and to persuade business political action committees to give to Democratic candidates.

In the past, safe Democratic incumbents have received a disproportionately large share of the money for Democratic candidates, while non-incumbent Democrats have often gone begging. The GOP has been far more effective in distributing money.

Separate studies of campaign finance by Michael J. Malbin and Thomas W. Skladony of the American Enterprise Institute, and by the citizens' lobby Common Cause, reached these conclusions:

* The high growth of spending in House races during past elections slowed considerably this year. "House candidates raised only 10 percent more through mid-October than they had at a comparable time in 1982. That compares with 40, 35 and 48 percent growth rates in previous election cycles, and for the first time, it was only slightly faster than the inflation rate," Malbin said.

From 1982 to 1984, total House candidate receipts grew from $145.2 million to $159.6 million

* The rate of spending for Senate candidates continued to explode, however. From 1982 to 1984, Senate candidate spending increased from $94 million to $124.3 million, a 32 percent increase, according to Common Cause.

The growth of Senate spending is even more striking because in 1984, the population of the states with Senate contests was smaller -- 86 million -- than for the states with contests in 1982, 125 million.

Much of the Senate spending increase came from Rockefeller's use of his fortune to finance a campaign that cost $9.4 million through Oct. 17 and from the fund-raising war between Sen. Jesse Helms (R-N.C.), who garnered $14.4 million, and Gov. James B. Hunt Jr., his unsuccessful challenger, who raised $8.6 million.

In the House, however, there were significant changes in the partisan patterns of fund-raising that suggest that Democrats are slowly catching Republicans in the effective distribution of money in tight contests.

A Washington Post analysis of 83 House races decided by 12 percentage points or less, and some races considered to be close by both parties, found:

* Democratic incumbents facing serious challenges outraised their Republican opponents by a wide margin. In 52 races, Democrats raised an average of $100,000 more than Republicans, $347,000 to $247,000.

But a separate analysis by Malbin of the 13 races among these 52 contests where the Democratic incumbent lost showed that the successful Republican challengers outspent the losing Democrat, $418,000 to $386,000.

In 1980, similar to 1984 in terms of a surge of GOP voting, many Democratic incumbents were caught financially flat-footed, unexpectedly outspent by Republican challengers.

Officials of the Democratic Congressional Campaign Committee contend that in Tuesday's election, the last-minute channeling of $50,000 to Rep. Bruce Morrison (D-Conn.) was critical to his 53-to-47 percent victory over former representative Lawrence DeNardis (R) in a contest where Morrison was able to raise $886,000 compared with $489,000 by DeNardis.

In contrast, one of the defeated Democratic incumbents, Rep. Bill Patman (D-Tex.), was not only outspent $432,000 to $235,000 by his opponent, David Sweeney (R), but he received just $97 from the Democratic Party, in a miscalculation that contributed to Patman's 49-to-51 percent loss.

* In 15 races for open seats in which the incumbent had retired or had been defeated in the primary, Democrats raised more money on average than Republicans, $353,000 to $301,000.

* In races where Democrats challenged Republican incumbents, Republicans had a decisive financial advantage, $415,000 to $286,000. In almost all cases, however, Democrats raised at least $200,000 by the Oct. 17 reporting date, enough for a credible race.

This is in sharp contrast to 1982, when many Democratic challengers in close contests raised considerably less than $200,000. The fund-raising weakness of the 1982 Democratic candidates is widely viewed by strategists in both parties as one of the reasons Republican House losses were kept to 26 at a time when the severe recession pointed toward larger Democratic gains.

"The story of 1982 was the Republican Party," Malbin said. "It kept losses well below expected levels" by carefully allocating resources to endangered incumbents, while the Democratic Party failed to channel support to many of its strong challengers.

On another front, the Democratic Party's national, congressional and senatorial committees succeeded this year in reversing a steady trend favoring the Republican committees.

For the three election cycles from 1977-78 to 1981-82, the Republican Party fund-raising advantage steadily grew, from a 3.4-to-1 ratio in 1977-78, $49.6 million to $14.4 million, to a 6.5-to-1 advantage in 1981-82, $161.2 million to $24.8 million.

In the 1983-84 election cycle, the Republican Party retained a strong advantage, $207.7 million to $59.7 million, but the advantage fell back to a 3.5-to-1 ratio. According to the Federal Election Commission, Democratic Party receipts have grown during the first 18 months of 1983-84 at a 141 percent rate, while GOP receipts grew by 29 percent.

The huge Republican dollar advantage, however, permitted the GOP to give $50,800, the maximum allowed under law, to about 75 House candidates, while the Democratic Congressional Campaign Committee "maxed out" in only two contests.

Mark Johnson, of the Democratic congressional committee, contended that it has gone from a "$1,000 committee," which gave only $1,000 to candidates in 1980, to an organization giving sizable amounts to numerous candidates. He provided a list showing that the committee gave almost $2 million to candidates, including more than $20,000 to 40 candidates.

In addition to giving much more money to candidates, the National Republican Campaign Committee was able to finance extensive polling, research and other forms of support to its candidates.